Charging iPhone in USA

If you have an Apple supplied (or other quality charge cube) it will be capable of accepting input voltages from 100-240 volts AC. If this is the case, you would simply need a plug adapter for the local power system.

The power adapter will run on 100-240 Volts and 50/60 Hz automatically, so it will work literally anywhere in the world.

Therefore, a voltage converter is not needed, but you will need a wall plug adapter to connect the UK plug to the US wall socket.

Amazon has them, or you can pay 3 times as much at the airport shops.